CVE-2026-90313 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf, cgroup: Fix invalid storage access after __cgroup_bpf_attach failed
A potential invalid storage access issue can occur after replacing a cgroup bpf prog.
This occurs in the following scenario: 1. prog1 with storage is attached to a cgroup in multi-attach mode. 2. prog1 is replaced with prog2 using BPF_F_REPLACE in multi-attach mode, but fails midway (e.g. in bpf_trampoline_link_cgroup_shim or update_effective_progs). 3. A new prog3 is attached to the cgroup in multi-attach mode.
The reason is that __cgroup_bpf_attach overwrites pl->storage with the new storage prior to attachment completion. When attachment fails midway, the cleanup path calls bpf_cgroup_storages_free(new_storage) to free the newly allocated storage, but fails to restore pl->storage back to old_storage.
Consequently, the still-active prog1 holds invalid or dangling storage pointers, leading to an invalid memory access when prog1 executes and calls bpf_get_local_storage. Additionally, original pl->flags and cgrp->bpf.flags[atype] are left unrestored.
Fix this by saving old_pl_flags, old_storage, and old_flags prior to the update, and properly restoring all of them in the cleanup path on error.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's BPF subsystem contains a critical vulnerability related to cgroup attachment operations that can lead to invalid memory access and potential system instability. This issue specifically affects scenarios involving multi-attach mode where eBPF programs are attached to control groups with associated local storage mechanisms. The root cause lies in the implementation of the __cgroup_bpf_attach function, which manages the lifecycle of BPF program attachments and their associated data structures. When a new BPF program is introduced to replace an existing one using the BPF_F_REPLACE flag, the kernel attempts to update internal pointers and flags before confirming successful attachment completion.
The vulnerability manifests during a specific sequence of operations where prog1 with storage is initially attached to a cgroup in multi-attach mode. Subsequently, an attempt is made to replace this program with prog2 using the BPF_F_REPLACE flag within the same multi-attach context. If this replacement operation fails midway through execution, such as during bpf_trampoline_link_cgroup_shim or update_effective_progs phases, the kernel's cleanup path incorrectly handles the state of storage pointers and flags. Specifically, __cgroup_bpf_attach overwrites pl->storage with new_storage before attachment completion is verified. When the operation aborts due to an error, the cleanup routine frees the newly allocated storage but fails to restore pl->storage back to its original value pointing to old_storage.
This failure in state restoration results in a dangling pointer scenario where the still-active prog1 retains references to freed or invalid memory locations. As a consequence, when prog1 executes and invokes bpf_get_local_storage, it accesses memory that is no longer validly allocated for this purpose. This constitutes an out-of-bounds read vulnerability as defined by CWE-125, which can lead to information disclosure if the accessed memory contains sensitive data from other processes or kernel structures. Furthermore, in more severe cases where subsequent writes occur through these invalid pointers, it could potentially escalate into arbitrary code execution vulnerabilities similar to CWE-787, although the primary immediate risk is instability and potential denial of service due to kernel oops or panic conditions triggered by illegal memory access patterns.
The operational impact extends beyond simple memory corruption risks because original pl->flags and cgrp->bpf.flags[atype] are also left unrestored during failed attachment attempts. This state inconsistency can cause subsequent BPF operations on the same cgroup to behave unpredictably, potentially bypassing security checks or causing further resource leaks. The vulnerability highlights a fundamental flaw in atomicity guarantees within the kernel's BPF subsystem, where partial failures do not result in proper rollback of all modified states. Attackers with local access who can trigger these specific attachment failure scenarios could exploit this inconsistency to destabilize the system or potentially escalate privileges if they can influence what data resides at the freed memory addresses through careful timing and allocation strategies.
From a threat modeling perspective, this vulnerability aligns with ATT&CK techniques related to privilege escalation via kernel exploitation, particularly those involving improper handling of resource management during state transitions. The lack of proper rollback mechanisms for complex multi-step operations represents a common pattern in kernel vulnerabilities that can be leveraged by malicious actors seeking to compromise system integrity. The issue underscores the importance of rigorous error handling and atomic transaction semantics in low-level systems programming where partial failures must not leave the system in an inconsistent or vulnerable state.
Mitigation strategies primarily involve applying vendor-provided patches that address this specific race condition and state management flaw. System administrators should ensure their Linux kernels are updated to versions containing fixes for this cgroup BPF attachment issue. For environments unable to immediately patch, restricting unprivileged users from attaching eBPF programs to control groups can reduce the attack surface significantly since local user access is typically required to trigger these specific multi-attach scenarios involving program replacement failures. Additionally, enabling kernel hardening features such as KASLR and stack protector mechanisms may mitigate exploitation attempts by randomizing memory layouts and detecting certain types of buffer overflows that might result from accessing invalid storage pointers.
Long-term remediation requires reviewing the BPF subsystem's attachment logic to ensure all state modifications are wrapped in proper rollback procedures upon failure. Developers should implement comprehensive error handling paths that restore pl->storage, old_pl_flags, and cgrp->bpf.flags[atype] to their pre-operation values whenever an attachment operation does not complete successfully. This ensures atomicity of the BPF program attachment process and prevents any intermediate states from persisting in memory where they could be exploited by subsequent operations or malicious actors attempting to leverage these inconsistencies for further compromise attempts within the kernel space.